Expiration date.

Some relationships expire and holding on to them past the best-by-date doesn't make them last longer, it just starts making you sick...

When milk goes bad, you don't keep it in the fridge, hoping that it will somehow make itself brand new. It's the same thing with friendships/relationships. Not everything is going to last. Not every person who comes into your life is meant to stay forever. It would be nice if people came with warnings or expirations date like spoiled milk but they don't. All you can do is try to enjoy them while they are around and be willing to let them go when they're time is up. It can be scary to find out you've been wrong about something or someone.. but we can't be afraid to change our minds and accept that things are different and may never be the same, for better or for worse. It isn't always easy and at times you will wonder if you've made the right choice by letting them go, but if they are meant to stay they will eventually come back. 

"What is truly yours would eventually be yours 

and what is not, no matter how hard you try, will never be yours."

And thats just how the world works...